Photophysical properties and computational investigations of tricarbonylrhenium(I)[2-(4-methylpyridin-2-yl)benzo[d]-X-azole]L and tricarbonylrhenium(I)[2-(benzo[d]-X-azol-2-yl)-4-methylquinoline]L derivatives (X = N–CH3, O, or S; L = Cl−, pyridine)

We report a combined experimental and computational study of new rhenium tricarbonyl complexes based on the bidentate heterocyclic N–N ligands 2-(4-methylpyridin-2-yl)benzo[d]-X-azole (X = N–CH3, O, or S) and 2-(benzo[d]-X-azol-2-yl)-4-methylquinoline (X = N–CH3, O, or S). Two sets of complexes are reported. Chloro complexes, described by the general formula Re(CO)3[2-(4-methylpyridin-2-yl)benzo[d]-X-azole]Cl (X = N–CH3, 1; X = O, 2; X = S, 3) and Re(CO)3[2-(benzo[d]-X-azol-2-yl)-4-methylquinoline]Cl (X = N–CH3, 4; X = O, 5; X = S, 6) were synthesized heating at reflux Re(CO)5Cl with the appropriate N–N ligand in toluene. The corresponding pyridine set {Re(CO)3[2-(4-methylpyridin-2-yl)benzo-X-azole]py}PF6 (X = N–CH3, 7; X = O, 8; X = S, 9) and {Re(CO)3[2-(benzo[d]-X-azol-2-yl)-4-methylquinoline]py}PF6 (X = N–CH3, 10; X = O, 11; X = S, 12) was synthesized by halide abstraction with silver nitrate of 1–6 followed by heating in pyridine and isolated as their hexafluorophosphate salts. All complexes have been fully characterized by IR, NMR, electrochemical techniques and luminescence. The crystal structures of 1 and 7 were obtained by X-ray diffraction. DFT and time-dependent (TD) DFT calculations were carried out for investigating the effect of the organic ligand on the optical properties and electronic structure of the reported complexes.